Trace analysis of trichlorobenzenes in fish by microwave-assisted extraction and gas chromatography–electron-capture detection

An analytical method consisting of extraction, clean-up, and analysis by gas chromatography–electron-capture detection (GC–ECD) was developed for the determination of trichlorobenzenes (TCBs) in fish samples. Two extraction methods, saponification and liquid–liquid extraction (S-LLE), and microwave-assisted extraction (MAE), were evaluated. In both cases, n-pentane was used as the extraction solvent. For S-LLE, the recoveries ranged from 66.6±9.1% for 1-bromo-4-chlorobenzene (4-BCB) to 93.5±4.9% for 1,2,4-trichlorobenzene (1,2,4-TCB). The recoveries were significantly lower, between 31.0±3.9% for 1,2,3-trichlorobenzene (1,2,3-TCB) and 52.3±3.0% for 1,3,5-trichlorobenzene (1,3,5-TCB), in the absence of fish. Proteins and glycerides of the fish tissue seemed to compete with TCBs for the base, and hence decreased their decomposition rate. In the case of MAE, the recoveries were highly dependent on the pressure applied during extraction. At 5 bar, much higher recoveries were obtained, from 66.7±15.6% for 4-BCB to 79.9±13.6% for 1,2,4-TCB, than at 1 bar. Sulfur formation was, however, observed at 5 bar, and interfered with the GC–ECD analysis of TCBs. Sulfur was adequately removed by copper powder treatment, which was shown not to affect the recovery of analytes. The recoveries of target analytes by S-LLE and MAE did not differ statistically (t-test, α=0.01). Both methods were appropriate for the detection of TCBs at concentration levels typically observed in marine biota, i.e. ∼1 ng/g. S-LLE was, however, more time consuming, and required larger volumes of high-purity organic solvents than MAE.